2,3 DPG binds to sites in hemoglobin and causes in its oxygen affinity:

Ans. D. One, decreasesThe Hemoglobin tetramer binds to one mol of 2,3 BPG in the central cavity formed by four subunits.2,3 BPG forms salt bridges with terminal amino group of both b globin chain via, Valine, Lysine and Histidine.Considering these two sentences, If central cavity is taken into account 2,3 BPG binds to one site.But actually 2,3 BPG is forming salt bridges with two beta subunit, so correctly it is binding to two b sites.So two is a better answer than four, for the number of binding site. As it is not there in the option, better answer is one.Binding of 2,3 BPG decreases the affinity of Oxygen towards HbHb F has low affinity towards 2, 3 BPG.